High loading electrodes

ABSTRACT

Provided are electrodes that may be used in electrochemical cells that incorporate relatively high loading of active material while also demonstrating excellent adhesion, resistance to mechanical breakdown, and also offer improved capacity retention, particularly at discharge rates of C/72 or greater.

CROSS REFERENCE TO RELATED APPLICATIONS

This application depends from and claims priority to U.S. ProvisionalApplication No. 62/346,799 filed Jun. 7, 2016, the entire contents ofwhich are incorporated herein by reference.

FIELD

This disclosure relates to high loading electrodes for use inelectrochemical devices such as secondary batteries.

BACKGROUND

The search for improved energy density is driven in part by everincreasing demand for electric vehicles with both increased range andlighter weight. To achieve this goal the power source for such vehiclesmust be capable of operating at a relatively high temperature, havinghigh energy density and exhibiting excellent cycle life characteristics.To address these needs, it may be helpful to increase amount of activematerial included into a battery of the same size.

Prior attempts to increase the areal loading or energy density of activematerials, however, has met with limited success primarily due toresulting issues of reduced adhesion and flexibility of the electrodethereby leading to cracking of the electrode decreasing cycle life. Assuch there is a need for electrodes with increased areal loading withoutsuffering from the reduced mechanical characteristics or reducedperformance of prior materials.

SUMMARY

The following summary is provided to facilitate an understanding of someof the innovative features unique to the present disclosure and is notintended to be a full description. A full appreciation of the variousaspects of the disclosure can be gained by taking the entirespecification, claims, drawings, and abstract as a whole.

Provided are electrodes that allow for greater incorporation of activematerial, i.e., high loading, while also demonstrating excellentadhesion and resistance to mechanical breakdown and improved capacityretention, particularly at discharge rates of C/2 or greater.Optionally, high loading electrodes as provided herein are characterizedby areal loading, electrochemical loading or both. An electrode is acathode or an anode. The loading of active material in a cathode may beand areal density of 30 mg/cm² or greater. The loading of activematerial in an anode may be areal density of 10 mg/cm² or greater. Theloading of active material for either a cathode or anode may be at orabove 4 mAh/cm². A characteristic of the electrodes as provided hereinin some aspects is an increased uniformity in binder distribution suchthat the increased binder migration toward the electrode surface ofprior electrode systems is reduced resulting in greater binderdistribution uniformity and/or increased binder concentration at theactive/current collector interface. For a cathode, the ratio of binderconcentration at a surface of the cathode active material relative tothe binder at a current collector substrate surface is 2.0 or lower. Foran anode, the ratio of binder concentration at a surface of the anodeactive material relative to the binder at a current collector substratesurface is 3.0 or lower, optionally 2.0 or lower. The ability to produceelectrodes with high active material loadings at this increased binderuniformity is believed to result in the improved adhesion and mechanicalcharacteristics of the resulting electrodes while also supportingimproved capacity retention.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects set forth in the drawings are illustrative and exemplary innature and not intended to limit the subject matter defined by theclaims. The following detailed description of the illustrative aspectscan be understood when read in conjunction with the following drawings,where like structure is indicated with like reference numerals and inwhich:

FIG. 1 is a representative image of an cathode dried using air (A) orusing VFM (B) and subsequently subjected to a mandrel test;

FIG. 2 is a representative image of an anode dried using air (A) orusing VFM (B) and subsequently subjected to a mandrel test:

FIG. 3 illustrates NCM 523 cathodes calendered to 40% porosity withloadings of 30 mg/cm² and 50 mg % cm² either dried under (A) hot air at120° C., or (B) using VFM techniques;

FIG. 4 illustrates the rate capability of cathodes formed usingtraditional air drying techniques or by VFM illustrating improvedcapacity retention of VFM dried electrodes:

FIG. 5 illustrates the rate capability of anodes prepared using either(A) water based binder or (B) NMP based binder demonstrating improvedcapacity retention of VFM dried electrodes;

FIG. 6 illustrates capacity retention of NCM 523 cathodes dried usingtraditional air techniques (hot air) or VFM (ADP) illustrating improvedcapacity retention for cathodes prepared using VFM techniques:

FIG. 7 illustrates through resistance of cathodes at various loadingdried using either traditional techniques (hot air) or using VFMtechniques (ADP);

FIG. 8 illustrates the AC impedance of cathodes loaded to 40 mg/cm² or50 mg/cm² and dried using either traditional air drying techniques (hotair) or by VFM (ADP);

FIG. 9 illustrates binder distribution of cathodes with solvent-basedPVDF binders illustrating greater uniformity of binder distribution whendried using VFM techniques as compared to traditional air dryingtechniques at loadings of 50 mg/cm²;

FIG. 10 illustrates binder distribution of anodes with water-basedCMC/SBR binders illustrating greater uniformity of binder distributionwhen dried using VFM techniques as compared to traditional air dryingtechniques; and

FIG. 11 illustrates binder distribution of anodes with solvent-basedPVDF binders illustrating greater uniformity of binder distribution whendried using VFM techniques as compared to traditional air dryingtechniques.

DETAILED DESCRIPTION

The following description of particular aspect(s) is merely exemplary innature and is in no way intended to limit the scope of the invention,its application, or uses, which may, of course, vary. The disclosure ispresented with relation to the non-limiting definitions and terminologyincluded herein. These definitions and terminology are not designed tofunction as a limitation on the scope or practice of the disclosure butare presented for illustrative and descriptive purposes only. While theprocesses or compositions are described as an order of individual stepsor using specific materials, it is appreciated that steps or materialsmay be interchangeable such that the description may include multipleparts or steps arranged in many ways as is readily appreciated by one ofskill in the art.

The terminology used herein is for the purpose of describing particularaspects only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “Or” means “and/or.” As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof. The term “or a combination thereof” means a combinationincluding at least one of the foregoing elements.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Provided are high loading electrodes that display improved energydensity. The electrodes show unexpectedly high adhesive properties andcapacity retention at rates at or equal to C/2. High loading as usedherein refers to the amount of electrode active material measured eitheras areal density of the electrode active material or electrochemicalloading. Optionally, a high loading electrode is one that has an arealloading of cathode active material of 30 mg/cm² or greater, optionally30 milligrams per square centimeter (mg/cm²) to 75 mg/cm², optionally 30mg/cm² to 50 mg/cm², or an anode active material areal loading of 10mg/cm² or greater, optionally 10 mg/cm² to 30 mg/cm², optionally 15mg/cm² to 25 mg/cm².

Optionally, high loading is defined by the electrochemical loading ofactive material. In such circumstances, a high loading electrode has anelectrochemical loading of 4 milliampere hours per square centimeter(mAh/cm²) or greater, optionally 4-15 mAh/cm², optionally 4-10 mAh/cm²,optionally at or greater than 4 mAh/cm², optionally at or greater than 5mAh/cm², optionally at or greater than 6 mAh/cm², optionally at orgreater than 7 mAh/cm², optionally at or greater than 8 mAh/cm²,optionally at or greater than 9 mAh/cm², optionally at or greater than10 mAh/cm².

The electrodes as provided herein include an electrochemically activematerial and a binder that are coated onto a current collector substrateeither directly on or via an intermediate substrate or material. Anelectrochemically active material is optionally suitable for use in acathode, such as a cathode active material. Optionally, anelectrochemically active material is optionally suitable for use in ananode, such as an anode active material. An “active material” is amaterial that participates in electrochemical charge/discharge reactionof the battery such as by absorbing or desorbing an ion such ashydrogen, lithium, sulfur or other ion. Optionally, an anode activematerial, cathode active, material or both are suitable for use in alithium ion cell. Optionally, an anode active material, cathode active,material or both are suitable for use in a lithium sulfur cell.Optionally, an anode active material is defined as an electrochemicallyactive material that will delithiate at potentials below 1.5 V versuslithium metal, optionally below 2.0 V versus lithium metal. Optionally,a cathode active material is defined as an electrochemically activematerial that will lithiate at potentials above 1.5 V versus lithiummetal, optionally above 2.0 V versus lithium metal. An anode activematerial or a cathode active material is optionally suitable for use inother cell types, optionally metal hydride cells, lead acid cells, ornickel-cadmium cells. Optionally, an anode active material or cathodeactive material is not suitable for use in one or more of metal hydridecells, lead acid cells, or nickel-cadmium cells.

The electrochemically active material is included in an electrode at ahigh loading. In some aspects, an electrochemically active material is acathode active material at an areal density of 30 mg/cm² or greater,optionally 30 mg/cm² to 75 mg/cm², optionally 30 mg/cm² to 50 mg/cm²,optionally at or greater than 30 mg/cm², optionally at or greater than35 mg/cm, optionally at or greater than 40 mg/cm², optionally at orgreater than 45 mg/cm², optionally at or greater than 50 mg/cm²,optionally at or greater than 55 mg/cm², optionally at or greater than60 mg/cm², optionally at or greater than 65 mg/cm², optionally at orgreater than 70 mg/cm². A cathode active material, is some aspects, isincluded in an electrode at an electrochemical loading of 4 mAh/cm² orgreater, optionally at or greater than 5 mAh/cm², optionally at orgreater than 6 mAh/cm², optionally at or greater than 7 mAh/cm²,optionally at or greater than 8 mAh/cm², optionally at or greater than 9mAh/cm², optionally at or greater than 10 mAh/cm².

In some aspects, an electrochemically active material is an anode activematerial at an areal density of 10 mg/cm² or greater, optionally 10mg/cm² to 30 mg/cm², optionally 15 mg/cm² to 25 mg/cm², optionally at orgreater than 11 mg/cm², optionally at or greater than 12 mg/cm²,optionally at or greater than 13 mg/cm², optionally at or greater than14 mg/cm², optionally at or greater than 15 mg/cm², optionally at orgreater than 16 mg/cm², optionally at or greater than 17 mg/cm²,optionally at or greater than 18 mg/cm², optionally at or greater than19 mg/cm², optionally at or greater than 20 mg/cm², optionally at orgreater than 21 mg/cm², optionally at or greater than 22 mg/cm²,optionally at or greater than 23 mg/cm², optionally at or greater than24 mg % cm², optionally at or greater than 25 mg/cm². An anode activematerial, is some aspects, is included in an electrode at anelectrochemical loading of 4 mAh/cm² or greater optionally at or greaterthan 5 mAh/cm², optionally at or greater than 6 mAh/cm², optionally ator greater than 7 mAh/cm², optionally at or greater than 8 mAh/cm²,optionally at or greater than 9 mAh/cm², optionally at or greater than10 mAh/cm².

The provided electrodes have a high loading of active material but alsoshow improved adhesion or capacity retention at discharge rates of C/2or greater than electrodes produced by prior techniques. Among thecharacteristics of the provided electrodes that result in the improvedproperties is optionally the binder distribution throughout theelectrode. Whereas prior high loading electrodes create a binderdistribution whereby the binder is somewhat segregated to higherconcentration at the surface of the electrode (distal from thesubstrate), typically 2 to 3 or more times the concentration binderpresent at the current collector surface, the provided electrodes have amore uniform binder distribution whereby the ratio of binder present atthe electrode surface relative to the substrate surface is less than 2for a cathode or optionally less than 3 for an anode. This more uniformbinder distribution produces an electrode that is more physically robustand less susceptible to cracking either during cell formation, handling,or cycling. At the same time, the resulting electrodes have bettercapacity retention.

Binder distribution is optionally defined as the amount (e.g.,concentration) of binder after drying between differing regions definedin a direction perpendicular to the substrate surface. In some aspects,the electrode thickness is separated into 5 zones with zone one (1)being the ⅕ of the electrode thickness nearest that current collectorsubstrate (proximal), and zone five (5) being the ⅕ of the electrodethickness nearest the electrode surface (distal the current collectorsubstrate) with zones 2, 3, and 4 distributed therebetween.

In some aspects whereby an electrochemically active material is acathode active material the concentration ratio of binder in zone 5 tozone 1.0 is 2.0 or lower, optionally 1.8 or lower, optionally 1.6 orlower, optionally 1.0 to 2.0, optionally 1.0 to 1.8, optionally 1.0 to1.6, optionally 1.0 to 1.5, optionally 1.0 to 1.4, optionally 1.2 to 2,optionally 1.2 to 1.8, optionally 1.2 to 1.6, optionally 1.2 to 1.5,optionally 1.2 to 1.4.

In some aspects whereby an electrochemically active material is an anodeactive material the concentration ratio of binder in zone 5 to zone 1 is3.0 or lower, optionally 2.5 or lower, optionally 2.3 or lower,optionally 2.0 to 3.0, optionally 2.0 to 2.8, optionally 2.0 to 2.5,optionally 2.0 or lower, optionally 1.8 or lower, optionally 1.6 orlower, optionally 1.0 to 2.0, optionally 1.0 to 1.8, optionally 1.0 to1.6, optionally 1.0 to 1.5, optionally 1.0 to 1.4, optionally 1.2 to 2,optionally 1.2 to 1.8, optionally 1.2 to 1.6, optionally 1.2 to 1.5,optionally 1.2 to 1.4.

In both an anode or cathode active material, the ratio of binder contentat a midpoint (zone 3) relative to zone 1 is 1.5 or lower, optionally1.4 or lower, optionally 1 to 1.5, optionally 1 to 1.4, optionally 1 to1.3, optionally 1.15 to 1.5, optionally 1.15 to 1.4, optionally 1.15 to1.3.

The resulting electrodes with high loading optionally have a cycle lifecharacterized by in excess of 80% residual capacity at cycle 20,optionally in excess of 80° % residual capacity at cycle 25, optionallyin excess of 80% residual capacity at cycle 50, optionally in excess of80% residual capacity at cycle 100, optionally in excess of 80% residualcapacity at cycle 150, optionally in excess of 80% residual capacity atcycle 200), optionally in excess of 80% residual capacity at cycle 250,optionally in excess of 80% residual capacity at cycle 300, optionallyin excess of 80% residual capacity at cycle 350, optionally in excess of80% residual capacity at cycle 400, optionally in excess of 80%,residual capacity at cycle 450, optionally in excess of 80% residualcapacity at cycle 500.

In some aspects, the capacity retention of an electrode is 90% orgreater when discharged at 0.5C rate, optionally 91%, 92%, 93%, 94%,95%, 96%, or 97% or greater when discharged at a 0.5C rate. Optionally,capacity retention of an electrode is 80% or greater when discharged at0.6C rate, optionally 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, or 89%, orgreater when discharged at 0.6C rate. Optionally, capacity retention ofan electrode is 50% or greater when discharged at 1C rate, optionally55%, 60%, 65%, 70%, 75%, 80%, or 85%, or greater when discharged at 1Crate.

An electrode includes an electrochemically active material. Anelectrochemically active material is optionally including or is formedfrom silicon, Ni, Co, Mn, Mg, Fe, Ti, Al, a rare earth metal, carbon(e.g. graphite etc.), a conductive additive such as a carbon additive,or combinations thereof. Optionally, an active material includes or is alithium nickel-cobalt-manganese oxide active material such as NCM-111,NCM-424, NCM-523, NCM-622, NCM-811 or lithium nickel cobalt aluminum(NCA). The amount of electrode active material is optionally present ata weight percent of 50% or greater relative to the binder.

An electrochemically active material is optionally suitable for use information of an anode or a cathode. In some aspects, anelectrochemically active material optionally is or includes silicon,graphitic carbon, silicon carbon composites, tin, Ge, Sb, Al, Bi, As, Limetal, lithium alloys, metal alloys, transition metal oxides, nitridematerials, sulfide materials, and combinations thereof. An alloyoptionally includes one or more of Mg, Fe, Co, Ni, Ti, Mo, and W.

Illustrative examples of a metal alloy for use as an electrochemicallyactive material include silicon alloys. A silicon alloy is optionallyand alloy of silicon and Ge, Be, Ag, Al, Au, Cd, Ga, In, Sb, Sn, Zn, orcombinations thereof. The ratio of the alloying metal(s) to silicon isoptionally 5% to 2000% by weight, optionally 5% to 500% by weight,optionally 20% to 60% by weight, based on silicon.

In some aspects, an electrochemically active material includes a lithiumalloy. A lithium alloy optionally includes any metal or alloy thatalloys with lithium, illustratively including Al, Si, Sn, Ag, Bi, Mg,Zn, In, Ge, Pb, Pd, Pt, Sb, Ti, tin alloys, and silicon alloys.

Additional examples of alloys and methods of alloy production can befound in U.S. Pat. No. 6,235,427.

In some aspects, the electrochemically active material is an anodeactive material. Illustrative examples of anode active materialsinclude: silicon; tin; carbon and graphitic carbon materials such asnatural graphite, graphene, artificial graphite, expanded graphite,carbon fibers, hard carbon, carbon black, carbon nanotubes, fullerenesor activated carbon; a composite material of a metal or metal compoundand a carbon or graphite material whereby a metal optionally includeslithium and silicon; or a lithium-containing nitride. Optionally, anelectrochemically active material is not graphite alone in the absenceof silicon, lithium, or a metal. In particular aspects, anelectrochemically active material is a composite material of silicon andgraphitic carbon that may or may not include a carbon coating and orthermal treatment to stabilize the adhesion of the coating to thesurface. In some aspects, an electrochemically active material includesa coating, illustratively a carbon coating. A carbon coating, whenpresent, is a component of an over coating on or directly on theelectrochemically active material.

In some aspects, an electrochemically active material is a cathodeactive material. Examples of a cathode active material include layeredcompounds such as lithium cobalt oxide (LiCoO₂) and lithium nickel oxide(LiNiO₂), or compounds substituted with one or more transition metals:lithium manganese oxides such as compounds of Formula Li_(1+x)Mn_(2−x)O₄(0≤x≤0.33), LiMnO₃, LiMn₂O₃ and LiMnO₂; lithium copper oxide (Li₂CuO₂);vanadium oxides such as LiV₃O₈, V₂O₅ and Cu₂V₂O₇; Ni-site type lithiatednickel oxides of Formula LiNi_(1−x)M_(x)O₂(M=Co, Mn, Al, Cu, Fe, Mg, Bor Ga, and 0.01≤x≤0.3); lithium manganese composite oxides of FormulaLiMn_(2−x)M_(x)O₂(M=Co, Ni, Fe, Cr, Zn or Ta, and 0.01≤x≤0.1), orFormula Li₂Mn₃MO₈ (M=Fe, Co, Ni, Cu or Zn); LiMn₂O₄ wherein a portion ofLi is substituted with alkaline earth metal ions; disulfide compounds;and Fe₂(MoO₄)₃; LiFe₃O₄; NCM based materials (e.g. NCM111, NCM424,NCM523, NCM622, NCM811); NCA (e.g. LiNi_(0.8)Co_(0.15)Al_(0.05)O₂); etc.

An electrochemically active material is optionally mixed with a binder.A binder is optionally a binder such as those used in secondarybatteries. Illustrative examples of binder materials include but are notlimited polyvinylidene difluoride (PVdF) optionally used in an n-methylpyrrolidone (NMP) solution, and styrene butadiene rubber (SBR) binderoptionally used in aqueous latex suspensions. Other illustrative bindermaterials include SBR/carboxymethyl cellulose (CMC) blends, CMC,polyacrylic acid (PAA), and polyvinyl alcohol (PVA). Some aspectsinclude systems in which the binder includes a partially or fullycrosslinked polyvinyl alcohol or derivative thereof. Other suitablebinders known in the art may be used in some aspects. Illustrativeexamples of a polymer material used in some aspects of a binder includepolyvinyl alcohol (PVA), polyacrylic acid (PAA), and polymethylmethacrylate (PMMA), or combinations thereof. Illustratively a polymeror copolymer that forms a component of a binder has a molecular weightof 10,000 Daltons or higher. Such polymers and copolymers (collectively“polymers”), optionally those containing PVA, PAA, or PMMA, arecommercially available. The polymers or copolymers optionally have ahigh polymerization degree, optionally of more than 3000.

Optionally, the amount of binder is limited in an electrode, optionallyto a weight percentage of 10 weight percent or less. Optionally, when anelectrode is a cathode, the weight percent of binder is 2% to 10%,optionally 3% to 5%, optionally 2%-10%, optionally 3%-10%, optionally4%-10%, optionally 5%-10%, optionally 6%-10%, optionally 7%-10%,optionally 8%-10%, optionally 9%-10%, optionally 3%, optionally 4%,optionally 5%, optionally 6%, optionally 7%, optionally 8%, optionally9%. Optionally, the amount of binder in a cathode does not exceed 10weight %, optionally 9 weight %, optionally 8 weight %, optionally 7weight %, optionally 6 weight %, or optionally 5 weight %. Optionally,when an electrode is an anode that is made with an aqueous bindersolvent, the weight percent of binder is 1% to 5%, optionally 2% to 4%,optionally 1%, optionally 2%, optionally 3%, optionally 4%, optionally5%. Optionally when an electrode is an anode that is made with anaqueous binder solvent, the weight percent of binder does not exceed 5weight %, optionally 4 weight %, optionally 3 weight %. Optionally, whenan electrode is an anode that is made with an non-aqueous binder solvent(e.g., NMP or other), the weight percent of binder is 2%-10%, optionally3%-5%, optionally 3%-10%, optionally 4%-10%, optionally 5%-10%,optionally 6%-10%, optionally 7%-10%, optionally 8%-10%, optionally9%-10%, optionally 3%, optionally 4%, optionally 5%, optionally 6%,optionally 7%, optionally 8%, optionally 9%. Optionally, the amount ofbinder in an anode that is made with an non-aqueous binder solvent doesnot exceed 10 weight %, optionally 9 weight %, optionally 8 weight %,optionally 7 weight %, optionally 6 weight %, or optionally 5 weight %.

The electrochemically active material prior to or following combinationwith a binder may be in any physical form such as a particulate (e.g.powder), nanowire, sheet, nanotube, nanofiber, porous structure,whisker, nanoplatelet, or other configuration known in the art.

In an electrode, an electrochemically active material is on or directlyassociated with a current collector substrate. A substrate is optionallyformed of any suitable electronically conductive and optionallyimpermeable or substantially impermeable material, including, but notlimited to copper, stainless steel, titanium, or carbon papers/films, anon-perforated metal foil, aluminum foil, cladding material includingnickel and aluminum, cladding material including copper and aluminum,nickel plated steel, nickel plated copper, nickel plated aluminum, gold,silver, any other suitable electronically conductive and impermeablematerial or any suitable combination thereof. In some aspects,substrates may be formed of one or more suitable metals or combinationof metals (e.g., alloys, solid solutions, plated metals).

An electrochemically active material is optionally in contact with abinder material, optionally intermixed with a binder material, in theformation of an electrode. The electrochemically active material isoptionally employed with a binder material when forming an electrode byprocesses readily understood in the art.

The resulting electrodes have a porosity which may be measured usingknown mass and calculated volume and related to actual final electrodevolume as a measure of free space within the electrode. When anelectrode is a cathode, a porosity is optionally 30% to 50% or any valueor range therebetween, optionally 35% to 40%. When an electrode is ananode, the porosity is optionally 20% to 4⁰% or any value or rangetherebetween, optionally 30% to 35%.

The electrochemically active material may be used in an electrode for aprimary or a secondary battery. An electrode is optionally fabricated bysuspending an electrochemically active material with a binder in asolvent to prepare a slurry, and applying the resulting slurry to acurrent collector substrate, followed by drying and optionally pressing.A solvent is optionally suitable to dissolve or suspend a binder. Asolvent for the slurry is optionally aqueous (predominantly water) ornon-aqueous (optionally excluding water). As such, water is an exemplarysolvent. Additional examples of the solvent used in preparation of theelectrode may include, but are not limited to carbonate-based,ester-based, ether-based, ketone-based, alcohol-based, or aproticsolvents. Specific organic solvents such as dimethyl sulfoxide (DMSO),N-methyl pyrrolidone (NMP) and ethylene glycol, and distilled water maybe used. Water or other aqueous solvents (e.g. buffered aqueous systems)may be used.

The electrode active material may be contacted with the currentcollector substrate via a continuous spray-coating or transfer coatingprocess and then subjected to drying.

Processes of forming a high loading electrode include a drying step.Drying is optionally performed substantially as described in U.S. patentapplication Ser. No. 14/385 in which a variable frequency microwave(VFM) drying/desiccation procedure is used to form an electrode.Briefly, a coated electrode that has not been subject to drying (oroptionally was predried or partially predried) is subjected to VFM in adesired atmosphere at a desired temperature for a time necessary tosufficiently dry the electrode for subsequent use in an electrochemicalcell. VFM is optionally swept in a range of 1 to 8 GHz, optionally 5 to7 GHz, optionally 5.85 GHz to 6.65 GHz. The VFM may be varied at anysuitable rate, optionally such that the rate of electrode transferthrough the VFM stage is subjected to one range of VFM during the dryingstep. VFM drying optionally takes place over 10 min or less.

Drying an electrode is optionally done in a gaseous atmosphere,optionally an inert gas atmosphere. An atmosphere optionally is orincludes nitrogen, argon, or other inert gas. Optionally, a gasatmosphere is or includes air.

Drying an electrode is performed at an atmospheric temperature. Anatmospheric temperature is the temperature of the atmosphere used to dryan electrode during a VFM drying process and is optionally 1 degreeCelsius (° C.) to 200° C., or any value or range therebetween.Optionally atmospheric temperature is 1° C. to 150° C., optionally 20°C. to 150° C., optionally 25° C. to 150° C., optionally 50° C. to 150°C., optionally 120° C., optionally 80° C.

An electrochemical cell is also provided that uses an electrode formedof an electrochemically active material at a high loading substantiallyas provided by the invention with aspects as described herein.

An electrochemical cell optionally further includes an opposingelectrode, optionally a cathode or an anode. The opposing electrode isoptionally formed by processes similar to those used to form the counterelectrode.

An electrochemical cell optionally includes a separator, optionallypositioned between an anode and a cathode. A separator is optionally anymaterial suitable for ion transfer. Optional separator materials includea polyolefin material (e.g. polyethylene (PE) and polypropylene (PP)),polyethylene terephthalate (PET), poly vinylidene fluoride (PVdF), amongothers.

An electrochemical cell includes an electrolyte. An electrolyte isoptionally a solid or fluid electrolyte. Illustratively, the electrolyteincludes a lithium salt and a non-aqueous organic solvent. A lithiumsalt is optionally LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiN(SO₂C₂F₅)₂.Li(CF₃SO₂)₂N, LiN(SO₃C₂F₅)₂, LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄, LiCl,LiI, or LiB(C₂O₄)₂ (lithium bis(oxalato) borate; LiBOB). The lithiumsalt is optionally present in a concentration ranging from about 0.1 Mto about 2.0 M. When the lithium salt is included at the aboveconcentration range, an electrolyte may have excellent performance andlithium ion mobility due to optimal electrolyte conductivity andviscosity. Other suitable electrolytes for other battery types may beused in the relative battery type (e.g., alkaline electrolyte such asKOH, solid electrolytes, among others).

Various aspects of the present invention are illustrated by thefollowing non-limiting examples. The examples are for illustrativepurposes and are not a limitation on any practice of the presentinvention. It will be understood that variations and modifications canbe made without departing from the spirit and scope of the invention.Reagents illustrated herein are commercially available, and a person ofordinary skill in the art readily understands where such reagents may beobtained.

EXPERIMENTAL

Components, Steps and Operation of Exemplary Aspects

Bench scale slurry casting was used to produce electrodes. The slurrymixing conditions were adjusted to obtain a coatable formulation forhigh energy cell electrode loading.

Cathodes are formed from 93 wt % lithium nickel cobalt manganese (NCMcathodes (532 or 622) as commercially available), 3 wt % conductivecarbon, and 4 wt % polyvinylidene fluoride (PVdF) dispersed in N-methylpyrrolidone (NMP). The components are mixed using a double planetaryRoss mixer (Charles Ross & Son Company) to make the slurry. In order toobtain thick electrodes, the solid content was adjusted to between50-65%. The slurry was casted at the desired loading on a 20-micronaluminum foil using a pilot scale slot-die coater. Control cathodes weredirectly dried at 120° C., optionally compressed by an automated IRM 200heated roll calender press then punched with matched-metal die to formthe positive electrode. Test cathodes were dried by subjecting thecoated cathodes to drying using VFM techniques. VFM drying was performedusing a frequency sweep from 5850 MHz to 6650 MHz with a sweep rate of100 msec. The sweep wave form was a sawtooth. The microwave power outputof the system was 2.25 KW TWT and the drying was performed at 95% maxrated power. Total microwave exposure time was 5 min. An aluminum stripwas welded to the foil of the dried electrode to serve as positiveterminal.

For production of an anode, a commercially available natural graphite(from Nippon Carbon Co.) with a capacity of 360 mAh/g was selected. Theanode active powder and a conductive carbon were mixed with either PVdFor SBR binder (Zeon, BM-400B) to make a slurry (solid content 35% to50%) by using a Flacktec SpeedMixer. The slurry viscosity and stabilitywere checked by using a rheometer (TA Instruments AR2000). Electrodeswere cast onto copper foil using a TMI K-control doctor blade coater anddried in a vacuum oven at 90° C., 120° C., or by VFM irradiation usingparameters as for the cathode.

Adhesion and Cohesion

The electrodes were qualified for adhesion and flexibility using thefollowing established standard operating procedures for productionelectrode quality assurance:

Mandrel Test:

The test unit was set up by placing a mandrel bar (size of 2, 3, and 4mm) between two rollers. An electrode sample was slit to 4″ long. Somesamples were calendered to a porosity of 40% and others were notcalendered. Holding each sample electrode at each end, the sample wasrolled back and forth over mandrel bar 5 or 6 times. The sample driedusing hot air only revealed significant surface cracking. By contrast inthe hot air dried samples, no cracking or delamination was observed onthe electrode surface dried using VFM at 80 degrees C. after the test(Grade 1, passed). The cathode results are presented in FIG. 1 and anoderesults depicted in FIG. 2. VFM in both anode and cathode produced highloading electrodes with excellent resistance to cracking anddelamination by handling relative to traditionally dried electrodes.

Wet Adhesion:

In a standard operation, three pieces of 2″×3″ electrode are soaked inan electrolyte at 85° C. for 2 hours while contained in a sealed pouch.The electrode is removed from the pouch and blotted dry with a papertowel. On patted-dry electrodes, the operator uses the end of a razorblade and gently scrapes the electrode using constant pressure. Aftermaking three scribes, the electrode is rotated to an angle of 90 degreesand three more scribes are made thus creating a cross hatch pattern. Theresulting electrodes are scored as follows:

1: No foil observed after all scribes are made

2: Foil is observed along the scribe line

3: Foil and flaking around crossed scribes observed

4: >⅔ of active material flakes off or total delamination

FIG. 3 shows the surfaces of cathodes made as above before and after thehot electrolyte test. The samples showed scraping marks only under therazor blade tips and only small delamination was observed (Grade 2)illustrating excellent wet adhesion of electrodes dried using VFMsimilar to those dried using traditional air drying techniques.

Cohesion

Cathodes made as above were subjected to cohesion testing. Samples ofthe electrode prepared as above were cut into square (3 cm×3 cm) andweighed. Electrodes were taped to a glass slide using double sided tape.A piece of KAPTON tape (10-15 cm) was placed on top of the electrode.Sample length and tape width were measured as well as the assemblyweight. The entire assembly was placed on a tensometer using cellclamps. The top clamp was moved at 20 mm/min with an average force of4N. The final assembly was weighed and samples were scored by mass lossper unit area and mass loss percentage with respect to initial electrodemass. Table 1 illustrates the results.

TABLE 1 Drying Loading Mass loss Method mg/cm² (wt %) Hot Air 30 0.8 502.4 VFM 30 0.7 50 2.5Electrochemical Properties

Electrode rate capability was also evaluated in Li half cells at 4.2 to2.7V. Cathodes made as above were calendered to 40% porosity targetthickness. The cell was charged at C/5 and discharged at differentC-rates. The cathodes were validated independently in coin half cellsversus lithium metal and in Li ion pouch cells versus baselineproduction-quality counter-electrodes. All the cells were assembledusing semi-automated pilot cell production equipment.

As the cathode loading increased to 30 mg/cm² or greater the VFM driedelectrodes showed improved performance compared to those prepared usinghot air drying only. At C/2 the electrodes with a loading of 50 mg/cm²were capable of similar capacity retention as a standard prepared 18mg/cm² loaded electrode. Results are illustrated in FIG. 4.

Anode: Similar protocols are performed using anodes prepared with eithera water based binder (SBR) or a solvent based binder (PVdF). When SBRbinder is used, the mass ratios were 97/2/1 wt % for activematerial/SBR/CMC (carboxyl methyl cellulose). When PVdF was used asbinder the graphite content was 94%. PVdF was 5% and conductive additive1%. Electrode rate capability was also evaluated in Li half cells 2.7 to4.2V. The cell was charged at C/5 and discharge at 0.1, 0.2, 0.5, and1.0C rates. The anode was tested against a Li metal counter electrode.The results are depicted in FIG. 5. Anodes prepared with both testedbinders electrodes prepared using VFM irradiation showed improved ratecapability.

Cycle Life: Cathodes prepared as above were evaluated in coin halfcells. The cells were cycled at C/2 rate between 4.2-2.7 V. Electrodeswere calendered to 40% porosity and annealed at 120° C. for 2 hours. Theelectrodes with high loading and dried using the VFM irriation processshowed improved cycle life relative to hot air dried electrodes. Resultsare illustrated in FIG. 6.

Resistance

Through resistance measurements were employed. Two ½″ gold plated diskssandwich the ½″ single coated electrodes. Resistance values (taken witha high precision multimeter) were taken at different pressures (10-70psi with compressed air) applied to plates. Electrodes formed using highloading and dried using VFM irradiation demonstrated lower resistancethan air dried electrodes. The results are illustrated in FIG. 7 showingreduced resistance in electrodes dried using VFM processes.

AC Impedance

Impedance measurements were performed using a Solartron SI 1287Electrochemical Interface and SI 1260 Impedance/Gain-phase Analyzer. TheNCM523 cathodes prepared as above using two loadings (40 mg/cm² and 50mg/cm²) were dried under either convection hot air (baseline) or with byVFM techniques. The cathodes were fabricated into Li half cells. Halfcells were charged to 4.3V for the impedance test, with frequencysweeping from 1 MHz to 1 mHz and with AC amplitude at 5 mV. Equivalentcircuit fittings were completed using the Z-view software to calculateOhmic resistance (R_(ohm)), surface resistance (R1), and diffusionresistance (Wo₁). The results are shown in FIG. 8 and numerical resultsin Table 2. Significantly reduced AC impedance was observed at both 40mg/cm² and 50 mg/cm² loadings.

TABLE 2 Cathode Loading (mg/cm²) 40 50 Drying method Hot air VFM Hot airVFM R_(ohm) 2.2 2.6 2.8 3.1 R1 (Surface/Charge Transfer) 16.1 13.8 16.612.5 Wo₁ (Diffusion/Mass 74.7 66.2 126.5 67.9 Transfer) R_(ohm) + R1 +Wo₁ 93 82.6 145.9 83.6Binder Distribution

Electrodes (anodes and cathodes) were subjected to measurements ofbinder distribution. The electrodes were divided into 5 regionsextending from zone 1 (the ⅕ thickness nearest the current collector) tozone 5 (the ⅕ thickness nearest the electrode surface distal from thecurrent collector). These zones are used when mapping (searching) forfluorine content (from the PVdF binder) using a scanning electronmicroscope (SEM) equipped with energy disperse X-ray spectroscopy (EDS)system. The EDS software (EDAX from Ametek) provides weight percent offluorine in the different zones giving a clear indication of binderdistribution. For cathodes with a loading of 50 mg/cm², the binderdistribution demonstrated greater uniformity throughout the electrode atall thickness zones as illustrated in FIG. 9.

Similar studies are performed with high loading anodes. For PVdF bindertesting was performed as above. In order to perform binder distributionon SBR binders, the anodes were stained with osmium using osmiumtetroxide (OsO₄) which is absorbed by the SBR binder. The presence ofthe heavy metal is sufficient to block the SEM electron beam clearlyrevealing SBR domains in the SEM image. Similar to the fluorine studiesabove, osmium metal was mapped in the different zones using EDS. Anodesusing SBR binder/water with 20 mg/cm² loading showed a modestly reducedratio of zone 5 binder to zone 1 w en compared to traditional air driedelectrodes. Anodes using SBR binder/water with 20 mg/cm² loadingdemonstrated greater uniformity than hot air dried electrodes asillustrated in FIG. 10. Similarly, anodes using NMP-based PVdF binderloaded to 20 mg/cm² showed a significantly lower zone 5/zone 1 ratio andgreater uniformity than hot air dried electrodes. Results areillustrated in FIG. 11.

Various modifications of the present disclosure, in addition to thoseshown and described herein, will be apparent to those skilled in the artof the above description.

Patents, publications, and applications mentioned in the specificationare indicative of the levels of those skilled in the art to which theinvention pertains. These patents, publications, and applications areincorporated herein by reference to the same extent as if eachindividual patent, publication, or application was specifically andindividually incorporated herein by reference.

The foregoing description is illustrative of particular aspects of theinvention, but is not meant to be a limitation upon the practicethereof.

The invention claimed is:
 1. An electrode comprising: anelectrochemically active material and a binder, the electrochemicallyactive material intermixed with the binder; the electrochemically activematerial coated onto a current collector substrate; i. wherein theelectrochemically active material is a cathode active material coated atan areal density of 30 mg/cm² or greater or at an electrochemicalloading of 4 mAh/cm² or greater, and the binder is distributed withinthe electrochemically active material such that the concentration ratioof binder at a surface of the cathode active material relative to thebinder at a current collector substrate surface is 2.0 or lower; or ii.wherein the electrochemically active material is an anode activematerial coated at an areal density of 15 mg/cm² or greater or at anelectrochemical loading of 5 mAh/cm² or greater, and the binderdistributed within the electrochemically active material such that theconcentration ratio of binder at a surface of the anode active materialrelative to the binder at a current collector substrate surface is 3.0or lower.
 2. The electrode of claim 1 wherein the electrochemicallyactive material is a cathode active material and the areal density is 30mg/cm² to 75 mg/cm².
 3. The electrode of claim 1 wherein theelectrochemically active material is an anode active material and theareal density is 10 mg/cm² to 30 mg/cm².
 4. The electrode of claim 1wherein the electrochemical loading is at or greater than 5 mAh/cm². 5.The electrode of claim 1 wherein the electrochemical loading is at orgreater than 6 mAh/cm².
 6. The electrode of claim 1 wherein theelectrochemically active material is a cathode active material and theratio is 1.8 or lower.
 7. The electrode of claim 1 wherein theelectrochemically active material is a cathode active material andwherein the ratio is 1.6 or lower.
 8. The electrode of claim 1 whereinthe electrochemically active material is an anode active material andthe ratio is 2.5 or lower.
 9. The electrode of claim 1 wherein theelectrochemically active material is an anode active material andwherein the ratio is 2.3 or lower.
 10. The electrode of claim 1 whereinthe binder is distributed within the electrochemically active materialsuch that a midpoint ratio or the amount of binder at a midpoint of theelectrochemically active material relative to the binder at a currentcollector substrate surface is 1.5 or lower.
 11. The electrode of claim10 wherein the midpoint ratio is 1.4 or lower.
 12. The electrode ofclaim 1 wherein the binder is an aqueous binder or a non-aqueous binder.13. The electrode of claim 1 wherein the electrochemically activematerial comprises Ni, Co, Mg, Mn, S, Al, Cu, Fe, Mg, B, Ta, V, or Ga,Si, carbon, or combinations thereof.
 14. The electrode of claim 13wherein the electrochemically active material comprises Ni and Co. 15.The electrode of claim 1 having a cycle life characterized by a residualcapacity in excess of 80% at cycle
 20. 16. The electrode of claim 1having a cycle life characterized by a residual capacity in excess of80% at cycle
 25. 17. The electrode of claim 1 having a capacityretention of 90% or greater at 0.5C rate.
 18. The electrode of claim 1having a capacity retention of 80% or greater at 0.6C rate.
 19. Theelectrode of claim 1 having a capacity retention of 50% or greater at 1Crate.
 20. A secondary cell comprising an electrode, the electrodecomprising an electrochemically active material and a binder, theelectrochemically active material intermixed with the binder; theelectrochemically active material coated onto a current collectorsubstrate; i. wherein the electrochemically active material is a cathodeactive material coated at an areal density of 30 mg/cm² or greater or atan electrochemical loading of 4 mAh/cm² or greater, and the binder isdistributed within the electrochemically active material such that theconcentration ratio of binder at a surface of the cathode activematerial relative to the binder at a current collector substrate surfaceis 2.0 or lower; or ii. wherein the electrochemically active material isan anode active material coated at an areal density of 15 mg/cm² orgreater or at an electrochemical loading of 5 mAh/cm² or greater, andthe binder distributed within the electrochemically active material suchthat the concentration ratio of binder at a surface of the anode activematerial relative to the binder at a current collector substrate surfaceis 3.0 or lower, or the cell comprising both i and ii.
 21. The electrodeof claim 1 wherein the areal density of the cathode active material orthe anode active material is on a single side of the current collectorsubstrate.